There are many different ways of mounting an NMO style amateur ham radio antenna. This same NMO mount also is commonly used on land mobile, or “logging road” radio antennas.
The 3/4” hole mount is one of the most popular. Simply screw the L bracket into the side fender of the vehicle, unscrew the top of the NMO mount, slip it into the hole, and screw the top back on to complete the mount. If you have access to the necessary machine tools you can also drill a 3/4” hole into a suitable size of metal (roof of vehicle) for example and also complete the mount. Personally I like the L bracket as it is less invasive and can be removed without leaving a large hole. This setup also provides a more permanent solution for those who will not need or want to remove the antenna or mount.
For those who prefer to not drill holes, but still want a semi permanent install the “trunk lip mount” is an excellent option. This mount relies on the trunk or hood to be flush with the body. Simply slip the mount under the side lip of the trunk or hood, and tighten the set screws. This provides a strong mount that can be removed with minimal effort, and also does not require drilling holes. However the side lip of the trunk or hood must be level.
Trunk Lip Mounts: https://www.fleetwooddp.com/search?type=product&q=trunk+lip+mount
For those who want an antenna that can be easily removed, the magnet mount is the way to go. These aren’t your grandmas fridge magnets, large and strong, these will keep your antenna stable while driving and can be easily removed and stowed away. Another advantage of the magnet mount is when placed on the roof of the vehicle, one will experience a slight improvement in performance compared to antennas that are mounted on the fender or hood, due to the extra foot or two higher the antenna is.
Magnet Mount: https://www.fleetwooddp.com/products/tram-g1239-nmo-antenna-magnet-mount-with-17-rg58-pl259-coax?_pos=1&_psq=g1239&_ss=e&_v=1.0
When it comes to semi tractor trucks the mirror mount is the king! This mount simply attaches to the side mirror of the truck along the rails of the mirror and is held in place either with U bolts or a back plate. This solution provides maximum robustness for any commercial truck driver. Most cases the mount can also be drilled into the side of the vehicle for the absolute maximum in stability. If you have a vehicle with roof rails or fender rails you can also attach the mount to those rails that are 1” or less in diameter. This provides a semi permanent solution that can be removed with some elbow grease.
Mirror Mounts: https://www.fleetwooddp.com/search?type=product&q=nmo+mirror+mount
Once your mount is connected to the vehicle ensure the coax is run to the radio in such a way that it is not bending at sharp angles, or is being pinched metal on metal. Generally drilling holes in the firewall is a good approach, or between the rubber gaskets of doors for not so permanent solutions. At times you may also have to attach the PL259 connector onto the end of the coax. This allows one to feed the cable through a smaller opening or use weatherproofing grommets. A good quality crimper will come in handy for this part, however it is possible to connect without one. Consult YouTube or Goggle for How-To’s or find the nearest “handy person” for assistance.
Remember, the antenna is one of the most important parts of any radio setup. A good quality, well positioned mount, will result in maximum efficiency and performance of your radio.